Above shortcut resulted in GPU details being popped up on my screen. SO it was bound to some other app which was overriding it. What worked for me is
-> check.
You need to go to Gaming > Global Settings > Performance Monitoring > Toggle Performance Logging Hotkey
You will see this is bound to Ctrl + Shift + O (so the shortcut is used - just buried).
To remove the shortcut (not an obvious process at all!) you need to click the Toggle Performance Logging Hotkey button, it will then ask to enter your hotkey, you then press delete - that is Del (not backspace, not esc or anything else - the Del key).